1. Field of the Invention
The present invention relates to a boiler, and more particularly, to a boiler which is preferable for reducing a concentration of CO, an unburned matter, an attached ash and the like near a side wall of a furnace.
2. Description of the Prior Art
In order to improve a heat efficiency of a boiler, it is necessary to reduce a concentration of a carbon monoxide (CO) and an unburned matter within a furnace. In order to reduce the concentration of CO and the unburned matter within the furnace, there has been known the following method.
A first method corresponds to a method of adjusting an operation condition, in particular, a method of adjusting an air flow amount in a burner and an air flow amount in an after air port for a two stage combustion.
A second method corresponds to a method of supplying an air to a space in which an unburned matter is increased. As an example of the second method, a method of supplying an air along a wall of a furnace is shown in Japanese Utility Model Unexamined Publication Nos. 59-92346 and 2-122909, and Japanese Patent Unexamined Publication Nos. 62-131106 and 3-286918.
Among these conventional examples, in Japanese Utility Model Unexamined Publication Nos. 59-92346 and 2-122909, and Japanese Patent Unexamined Publication No. 3-286918, there is disclosed a boiler in which an air port is provided in a lower portion of a burner stage.
In Japanese Patent Unexamined Publication No. 62-131106, there is disclosed a boiler in which the air ports are provided on four walls of the furnace and the air ports are provided on upper and lower portions and an intermediate height of a plurality of burner stages.
Inventors have verified an effectiveness of the conventional first and second methods mentioned above on the basis of a measurement and a numerical analysis of an actual boiler. As a result, it has become apparent that the concentration of CO and the unburned matter in the combustion gas have been still high near the side wall crossing to the wall having the burner at least at a height of the burner stage, even when any of these methods is employed. Further, it has become apparent that the ash is attached to the side wall in the case of burning a coal.
The reason is that the combustion gas generated from the burner comes near the side wall crossing to the wall having the burner since the pressure near the side wall is lower than that of the combustion area at the center of the furnace.
A countermeasure thereof is shown in Japanese Patent Unexamined Publication No. 7-98103. In this example, there is suggested a boiler comprising a plurality of burners and a plurality of air inlet ports for a two stage combustion disposed downstream of the burners, which is structured such that an auxiliary combustion port for supplying a gas for combustion having an oxygen partial pressure of 10% or less is provided between a side wall of a furnace and a burner so as to adjust an injection amount of the gas for combustion injected from the auxiliary combustion port and a direction of a jet, thereby preventing a burner jet from returning to the side wall of the furnace.
However, in this prior art, a pipe for supplying the gas for combustion having the oxygen partial pressure of 10% or less to the auxiliary combustion port is required. Since it is necessary to arrange a pipe for supplying the gas for combustion having a length of about some tens meters, a great cost increase can not be avoidable.
An object of the present invention is to provide a boiler structured such as to prevent a combustion gas from coming near a side wall by using an air, an oxygen, a combustion exhaust gas and the like.
The present invention provides a boiler comprising a combustion chamber formed by front and rear walls and a side wall crossing to said front and rear walls and a plural stages of burners placed on at least one of said front and rear walls, in which in order to make a pressure of a gas within said combustion chamber higher in a portion near the side wall than at a center portion of said combustion chamber, a gas port is provided between an outermost row burner and said side wall within a range of a height of said burner stages.
The present invention also provides a boiler comprising a combustion chamber formed by front and rear walls and a side wall crossing to said front and rear walls and a plural stages of burners placed on at least one of said front and rear walls, in which in order to make a pressure of a gas near said side wall within said combustion chamber higher than a pressure of a gas at a center portion of said combustion chamber, a gas jet port is provided in said side wall within a range of a height of said burner stages.
The present invention further provides a boiler comprising a combustion chamber formed by front and rear walls and a side wall crossing to said front and rear walls, a plural stages of burners placed on at least one of said front and rear walls and an after air port for a two stage combustion disposed downstream said burner stages, wherein at least one stage gas jet port for making a pressure of a gas near said side wall within said combustion chamber higher than a pressure of a gas at a center portion of said combustion chamber is provided between an outermost row burner and said side wall within a range of a height of said burner stages and a plural stages of gas jet ports are provided between said lowermost stage burner and said after air port.
In each of the boilers mentioned above, it is desirable that said gas port is provided at portions of said opposing front and rear walls, said portions having the same height, and wherein gas supply means for injecting said jet at a speed at which a gas jet from said opposing gas port collides in the middle of said front and rear walls is provided.
The present invention, more particularly, provides a boiler as cited in any one of the structures mentioned above, comprising supply means for supplying a pulverized coal as a fuel and an air for transferring said pulverized coal to said plural stages of burners, and supply means for supplying an air for combustion to said plural stages of burners and supply means for supplying a gas for jetting to said gas port, in which there is provided control means for controlling a flow amount of the jet from said gas port on the basis of a load demand of said boiler and a coal type information so as to reduce a flow amount of the jet from said gas port when a load of said boiler is low and increase a flow amount of the jet from said gas port in accordance that the load of said boiler becomes higher.
The present invention further provides a boiler as cited in any one of the structures mentioned above, comprising supply means for supplying a pulverized coal as a fuel and an air for transferring said pulverized coal to said plural stages of burners, and supply means for supplying an air for combustion to said plural stages of burners and supply means for supplying a gas for jetting to said gas port, in which measurement means for measuring a concentration of a carbon monoxide (CO) in a combustion gas near said side wall is provided, and there is provided control means for controlling a flow amount of the jet from said gas port on the basis of a load demand of said boiler and a measured result of said concentration of CO so as to reduce a flow amount of the jet from said gas port when a load of said boiler is low, increase a flow amount of the jet from said gas port in accordance that the load of said boiler becomes higher and reduce a flow amount of the jet from said gas port when said concentration of CO is equal to or less than a predetermined value.
The control means may be means for increasing the flow amount of said jet in accordance with a lowness of a fuel ratio in a pulverized coal.
The supply means for supplying the gas for jetting to said gas port may be means for branching the air for combustion of said burner so as to make the air for jetting. In this case, it is preferable that a flow amount adjusting damper is provided in each of a flow passage of the air for combustion and a flow passage of the air for jetting.
The supply means for supplying the gas for jetting to said gas port may be means for branching the air for transferring said pulverized coal so as to make the air for jetting.
In the case that an after air port for a two stage combustion is placed downstream said burner stage, the supply means for supplying the gas for jetting to said gas port can be means for branching the after air so as to make the air for jetting.
In accordance with the present invention, since in a boiler comprising a combustion chamber formed by front and rear walls and a side wall crossing to said front and rear walls and a plural stages of burners placed on at least one of said front and rear walls, in order to make a pressure of a gas within said combustion chamber higher in a portion near the side wall than at a center portion of said combustion chamber, a gas port is provided between an outermost row burner and said side wall within a range of a height of said burner stages, it is possible to increase a pressure of the gas near the side wall so as to prevent the combustion gas from coming close to the side wall, thereby reducing an attachment of the ash due to a collision of the combustion gas, a concentration of CO at an outlet of the combustion chamber and an unburned matter.